[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 240538
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0605 UTC Fri Sep 24 2021

Tropical Weather Discussion for North America, Central America
Gulf of Mexico, Caribbean Sea, northern sections of South
America, and Atlantic Ocean to the African coast from the
Equator to 31N. The following information is based on satellite
imagery, weather observations, radar and meteorological analysis.

Based on 0000 UTC surface analysis and satellite imagery through
0530 UTC.

...SPECIAL FEATURES...

Tropical Storm Sam continues to rapidly gain strength well east of
the Lesser Antilles. As of 24/0300 UTC, it is centered near 11.2N
40.9W or about 1355 nm ESE of the Northern Leeward Islands moving
W at 13 kt. Estimated minimum central pressure is 997 mb. Maximum
sustained wind speed is 60 kt with gusts to 75 kt. Satellite
imagery depicts numerous moderate to strong convection within
about 50 nm of the center. Scattered moderate to strong
convection is elsewhere in bands within 240 nm N and 120 nm S
semicircles. Peak seas are currently near 17 ft and are forecast
to increase to near 24 ft by Saturday morning. Sam is
moving toward the west, and this motion with a decrease in
forward speed is expected through Saturday. A motion toward the
west-northwest at an even slower forward speed is expected late
Saturday into Sunday. Rapid intensification is forecast to
continue through early Saturday. Sam is likely to become a
hurricane very soon and then could be a major hurricane by Friday
night or early Saturday. Please, read the latest HIGH SEAS
FORECAST issued by the National Hurricane Center at website-
https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml and the latest Peter
NHC Forecast/Advisory and Public Advisory at www.hurricanes.gov
for more details.

A gale-force, non-tropical low pressure system, the remnants of
Odette, is located near 44N42W, or a little more than 525 nm
west-northwest of the westernmost Azores. Showers and
thunderstorms remain limited near the low, and this system has
only a brief window of opportunity to become a subtropical or
tropical cyclone while it moves generally south-southeastward over
marginally warmer waters. Strong upper- level winds are expected
to develop over the system by late today, which should then limit
further development. Additional information on this system,
including gale warnings, can be found in High Seas Forecasts
issued by the Ocean Prediction Center ocean.weather.gov. Also see
the latest Tropical Weather Outlook at www.hurricanes.gov for more
details.

...TROPICAL WAVES...

An Atlantic tropical wave has its axis along 24W, south of 20N,
and it is moving W at 10 kt. Scattered moderate convection is
noted in the southern part of the wave from 08N to 12N and between
20W and 28W. The northern part of the wave is embedded in dry
Saharan air, inhibiting the development of showers and
thunderstorms.

A second Atlantic tropical wave has its axis along 55W, south of
20N, and it is moving W at 10-15 kt. Scattered moderate
convection is observed from 11N to 15N and between 53W and 58W.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis passes through coast of Senegal near
14N16W to 06N27W. A segment of the ITCZ extends from 06N27W to
07N36W and another segment continues from 07N43W to 0753W. Aside
from convection associated to the tropical waves and Sam described
above, scattered moderate convection is seen from 02N to 08N and
between 27W and 37W.

GULF OF MEXICO...

The main feature of interest in the Gulf of Mexico is frontal
boundary that traverses the basin from SW Florida to Veracruz. The
front is analyzed as stationary in the Gulf as of 0300 UTC.
A few showers and isolated thunderstorms are noted along the
boundary, with the strongest activity near the coast of Veracruz.
The air behind the front is quite dry, allowing fairly tranquil
weather conditions front Texas to Florida in the N Gulf. Recent
scatterometer satellite data show fresh NE winds behind the
frontal boundary in the central Gulf, especially from 25N to 28N
and between 85W and 90W. Fresh to locally strong N-NE winds are
depicted in the SW Gulf, especially near the coast of Veracruz.
Seas behind the front are 4-6 ft and 2-4 ft ahead of the boundary.

For the forecast, the stationary front extends across the southern
portion of the basin and it forecast to dissipate by Sat. Fresh
to strong winds will follow the front into tonight along the coast
of Veracruz where seas will be near 8 ft. Looking ahead, winds
and seas will diminish across basin from Sat and into early next
week as high pressure builds over the northern Gulf.

CARIBBEAN SEA...

A sharp upper-level trough extends from the vicinity of the
southeastern Bahamas to across eastern Cuba and to the
southwestern Caribbean. A surface trough is analyzed in the W
Caribbean extending from W Cuba to 13N81W near the island of San
Andres. This is allowing for the development of afternoon and
evening thunderstorms across the western and central Caribbean
Sea. A few thunderstorms still persist east of the Isle of Youth
in Cuba and over N Haiti. Isolated moderate convection is also
noted in the SW and south-central Caribbean, especially near the
northern coast of Colombia. A recent scatterometer pass indicate
fresh trades within 130 nm of the coast of NW Venezuela, including
the waters surrounding the ABC islands, while the rest of the
basin enjoys gentle to moderate trades. Seas in the central and E
Caribbean are 2-4 ft, while 1-2 ft are found elsewhere.

For the forecast, Tropical Storm Sam near 11.2N 40.9W 997 mb at 11 PM
EDT moving W at 13 kt. Maximum sustained winds 60 kt gusts
75 kt. Sam will strengthen to a hurricane near 11.4N 42.9W Fri
morning, move to 11.8N 45.0W Fri evening, 12.1N 46.6W Sat
morning, 12.5N 47.8W Sat evening, 13.0N 49.1W Sun morning, and
13.5N 50.4W Sun evening. Sam will change little in intensity as
it moves to 15.3N 53.2W by late Mon. Meanwhile, moderate trade
winds will persist over much of the Caribbean into early next
week, becoming fresh over the south- central Caribbean starting
Fri night as high pressure builds east of the Bahamas. Fresh to
strong winds are forecast in the Gulf of Honduras Sun night.

ATLANTIC OCEAN...

Please read the Special Features section above for details on
Tropical Storm Sam.

The Cumbre Vieja volcano on the island of La Palma in the Canary
Islands has been erupting since 19/1410 UTC. A significant ash
emission is ongoing in the vicinity of the volcano below 10,000 ft.
Marine and aviation interests should monitor this on-going
situation by reading Volcanic Ash Advisory issued by Meteo-France
at http://vaac.meteo.fr/volcanoes /la- palma/. The next advisory
will be issue no later than 24/0900 UTC.

A cold front extends from the E coast of Florida near 28N80W,
across the eastern seaboard of the United States to an
extratropical cyclone over the Great Lakes. A pre-frontal trough
is noted just ahead of the cold front from 31N77W to South
Florida. Scattered moderate to isolated strong convection is
observed on satellite imagery N of 24N and W of 72W. Recent
satellite-derived wind data show fresh to locally strong SE-S
winds from 27N to 31N and between 73W and 76W. Seas in this region
are 3-6 ft.

Another area of interest is a sharp surface trough extending from
31N60W to 25N65W and the 1009 mb remnant low of Peter near
23N67W. The interaction of these features with an upper level low
near Bermuda is inducing a large area of showers and
thunderstorms, especially from N of 20N and between 57W and 65W.
Scatterometer wind data indicate fresh to strong cyclonic winds
near the northern end of the surface trough, N of 28N. Seas in
this region are 5-8 ft, with the highest seas noted near the
highest winds.

Farther east, the 1010 mb remnant low of Rose is located near
28N42W and showers and thunderstorms are noted within 265 nm east
of the center. A weakening stationary front is observed from
31N46W to 27N54W and only a few showers are seen near the
boundary. Fresh northerly winds are found off the coast of
Mauritania, mainly E of 20W. A large area of northerly swell that
is producing 8-12 ft seas N of 22N and between 35W and 60W. Aside
from the features and related winds and seas already mentioned in
this discussion, moderate to occasionally fresh trade winds are
noted across the basin along with 4 to 6 ft seas in open waters.

For the forecast west of 65W, a cold front extending from 31N77W
to 28N80W will stall overnight, then dissipate through early Sun
just before a second weak front possibly moves into the region
late Sun. Farther east, Tropical Storm Sam near 11.2N 40.9W 997 mb
at 11 PM EDT moving W at 13 kt. Maximum sustained winds 60 kt
gusts 75 kt. Sam will strengthen to a hurricane near 11.4N 42.9W
Fri morning, move to 11.8N 45.0W Fri evening, 12.1N 46.6W Sat
morning, 12.5N 47.8W Sat evening, 13.0N 49.1W Sun morning, and
13.5N 50.4W Sun evening. Sam will change little in intensity as it
moves to 15.3N 53.2W by late Mon. .

$$
DELGADO
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